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Page:Popular Science Monthly Volume 21.djvu/372

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360
THE POPULAR SCIENCE MONTHLY.

thus indicated is manifestly sufficient to fill all demands, far into the future years, and this refers only to that which is now on the surface; while the experience gained at Hachinhama seems to show quite conclusively that, were all the present store removed, its place would be refilled with a new crop drawn from the inexhaustible resources beneath.

To explain the manner in which these separate deposits have been formed is not easy, though in relation to the two borates the following suggestions may possibly be of some avail: If in a broad, shallow, mud-bottomed lagoon, the sodium of which has already formed its combinations with carbonic acid and chlorine, we imagine the process of evaporation to continue until instead of water there remains merely a muddy mass, so far viscid as to be unable to flow from one point to another, and that into this mass boracic acid is forced from beneath in. jets, here and there, only in limited areas, and not extending beyond them, and if we imagine, still' further, that the supply of boron is not sufficient to displace all the carbon and chlorine, we should have carbonate and chloride existing, intermingled with borate of soda, precisely as we in fact find them, and with a lime-mud we would have the ulexite.

This may perhaps answer for the borates, but a much greater difficulty is encountered when we propose to ourselves the question how the carbonate and the chloride crystallized separately. Over the chief extent they are blended, as they would be left by the evaporation of a lake which held them both in solution. Yet it is also true that, here and there, in areas separated from each other by no elevations whatever, and which have evidently never been separated, but which must have been parts of the same lake, vast beds of pure salt occur; while, perhaps, a quarter or half a mile away, carbonate of soda is lying in equally great quantity. How can these masses have been thus placed? Their bulk demonstrates that in each case quite a considerable depth of solution, even in its most concentrated form, was absolutely necessary. They could not have existed in such juxtaposition and have retained their chemical integrity.

Could the deposits have been formed at different times? There is nothing to indicate it, nor is the difficulty made less by answering this question in the affirmative. The chloride, in a blended solution, would of course be the last to crystallize, yet there is nothing to cause us to believe that over the carbonate-beds a mass of salt was once formed and subsequently removed. Neither can the two salts be crystallized in bulk, from a united solution, by any means with which we are at present acquainted, and left in the state of separate purity, in which countless thousands of tons are now lying on the deserts of Nevada.

The question is as difficult as the one why the mud of Borax Lake is filled with the green crystals, while that of Hachinhama has none.